Various systems for molding thermoplastic materials into a variety of forms are known. For example, U.S. Pat. Nos. 6,900,547, 6,869,558, 6,719,551 and U.S. Patent Application Publication No. 2004/0253429, each to Polk, Jr. et al., disclose a thermoplastic molding system including a thermoplastic extrusion die for the extrusion of a thermoplastic slab profiled by adjustable die gate members. The adjustable die gate members are dynamic die settings for varying the thickness of the extruded material in different parts of the extruded slab. The thermoplastic extrusion die has a trimmer for cutting the extruded thermoplastic slab from the thermoplastic extrusion die. A plurality of thermoplastic molds, which may be either vacuum or compression molds, are each mounted on a movable platform for moving one mold at a time into a position to receive a thermoplastic slab being trimmed from the thermoplastic extrusion die. A molded part is formed with a variable thickness from a heated slab of thermoplastic material being fed still heated from the extrusion die.
Such molding systems have been previously used to mold various parts such as pallets, beams and backboards. However, the use of such a molding system to produce large panels for use as flooring, floor coverings, walls, wall coverings, ceilings and ceiling coverings has been limited due to the fact that such large panels made according to above-described method are prone to warpage.
In order to overcome this limitation of thermoplastic parts, large structural components are often constructed from concrete, steel, wood and other various materials. However, each of these materials suffers from a variety of limitations when used to construct structural components. For example, pre-cast concrete structural components are extremely heavy, bulky, costly and difficult to transport to the site of construction due in part to their bulkiness and heavy weight. In addition to construction and shipping difficulties with concrete structural components, the low tensile strength of concrete can result in failures in such components. Reinforcement is often required in such concrete structural components when subjected to large loads, thereby increasing the cost to manufacture such components.
Steel structural components also suffer from various deficiencies. For example, steel is quite heavy and costly to ship and can share construction difficulties with concrete as described.
Structural components built from wood also have a variety of limitations. Wood components are susceptible to environmental attacks, especially rot from weather and termites. In such environments, wood encounters a drastic reduction in strength, which compromises the integrity of the structure.
Accordingly, a need exists for a structural panel that is low-cost, lightweight and easily assembled. A further need exists for a process for forming such panels that allows for panels with a large size to be manufactured easily. A need also exists for a structural panel that has high warpage resistance and resistance to heavy traffic.